Defects in DNA repair and related functions have been implicated in several forms of human cancer. This includes, for example, genes directly involved in mismatch and nucleotide excision repair as well as genes that link repair mechanisms to other cellular processes such as cell cycle control. Deletions are a common type of mutation found in genes associated with cancer. The goal of this research project is to better understand deletion mutagenesis by studying this process genetically in S. cerevisiae. Mutator assays designed to specifically detect deletions will be constructed and used to determine if various genes that participate in DNA metabolic processes influence deletion mutagenesis. These deletion mutator assays will also be used in genetic screens to identify novel genes involved in deletion mutagenesis. RAD51 is a member of the RAD52 epistasis group and influences DSB repair, as well as other DNA metabolic processes. Repair of DSB's is believed to be a common mechanism of generating deletions. Furthermore, recent studies in mice suggest that Rad5l may also influence tumorigenesis. Here, a synthetic lethal screen will be used to identify genes involved in RAD51-mediated processes. This screen is likely to identify genes involved in deletion mutagenesis as well as other DNA repair and/or related processes. Genes recovered from both genetic screens will be characterized for their roles in deletion mutagenesis in several ways. This will include construction of various single and double mutant strains and subsequent analysis using the deletion mutator assays. The knowledge gained from this research project should improve our understanding of the mechanism(s) involved in deletion mutagenesis. A future goal is to apply this knowledge to the creation of animal models for the study of deletion mutagenesis and its importance in cancer.